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Energy: Worksheet 3
Do the following for #s 1 – 4:
1) Assume friction to be negligible unless otherwise indicated.
2) Sketch qualitative energy bar graphs for the original and final situations.
3) In the space below your graphs, display the system’s energy flow (KE, PE, PEs, W, Q, R).
1. A cart traveling at 5m/s hits a spring. When the car stops moving, how far is the spring compressed?
Final
Original
KE
PE PEs
KE PE
PEs
0
0
height (m)
2. Assuming 10% of the system’s energy is lost to heat via friction, what is the cart’s final velocity?
vo = 0
Final
Original
KE
5
m = 20 kg
PE PEs
KE PE
PEs
v=?
0
0
0
3. A block is placed on a spring, compressing it 0.3m. How high does the block go after the launch?
m = 500 g
v=0
k = 100
Final
Original
KE PE PEs
KE PE
N
m
0
x = 0.3 m
Original
Final
©Modeling Workshop Project 2006
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0
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Unit VII ws3b v3.0
PEs
4. The bullet strikes a block of wood which exerts an average force of 50,000N on the bullet.
How far does the bullet penetrate the wood? Assume the bullet’s PEo = 0J.
Final
Original
PE PEs
KE
Original
KE PE
PEs
Final
0
0
5. A person pulls a 50kg box pictured below with a force of 100N. The coefficient of friction is 0.15.
a) Sketch a force diagram for the box.
b) How much of the force acts in the direction of motion?
How much energy is transferred (via work) by the person as he pulls the box a distance of 10m?
c) Find out if the box moves at a constant speed. What does this say about the KE of the system?
d) Here energy is added to the system through work via the man’s applied force.
Energy is also subtracted from the system through heat via friction.
Which energy transfer, if any, is larger? How do you know?
©Modeling Workshop Project 2006
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Unit VII ws3b v3.0
6. Eric (m = 75kg) jumps off a 10m high cliff at Red Granite Quarry into the water below.
a) Determine his potential energy at the top of the cliff.
b) How much kinetic energy does he possess at impact? What is his velocity at impact?
c) Repeat steps a and b for Alison (m = 60kg).
7. A spring of constant 850N/m is compressed 0.4m. How fast can it make a 500g ball go?
8. A 10g bullet is fired from a rifle with a barrel that is 85cm long.
If the average force exerted by the expanding gas is 5500N, how fast will the bullet go?
9. A 24kg child goes down a 5m high slide and reaches the ground with a speed of 2.8m/s.
How much energy was lost to heat via friction in the process?
10. Wyle Coyote (m = 20kg) is shot out of a canon straight up with an original velocity of 50m/s.
a) Assuming that all his original kinetic energy was fully transferred into his final potential energy,
what is the maximum height he could reach?
b) Suppose that 20% of his original kinetic energy was lost via heat due to air friction.
Now what is the maximum height Wyle can reach?
©Modeling Workshop Project 2006
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Unit VII ws3b v3.0